In
Engineering 305 at
Humboldt State University, each student is
required to work on a
project (preferably through to it's completion) related to
appropriate technology,
or AT, which is the main bulk of the coursework. The project should be extensive
in hours of labor and information presented in a final report. Though there are
no specific criteria for what a project can be, they should prove a student's
effort in research, construction, and follow through. Projects are approved by
the course instructor.
Liz and I (John) chose to build an Earthen Oven. Just what is an Earthen Oven? It's an oven created by mixing clay, sand and fiber in varying proportions and usually in three layers.The first layer, the thermal layer, is made mostly of clay and sand. It is best when created in a dome shape providing heat for the oven by retaining heat from a fire that is first lit inside. The second layer, the insulation layer, is made mostly of fiber and clay. It covers the thermal layer helping prevent heat loss. The optional third layer, the outer layer, is made of clay, sand and fiber. It protects the first two layers from the elements and can be used to sculpt the oven into almost any shape. Earthen ovens provide an even source of all three types of heat (conduction, convection and radiation) to bake to perfection. This technology has existed for thousands of years and has been used by cultures worldwide. Some ovens in England are over 500 years old; this is not unusual if protected from the elements. The ovens are made of the earth - dirt - and dirt lasts a long time.
The ovens work in the following way: A small fire is lit inside the oven. The oven gains the heat from the fire. The fire/coals are removed once the oven has reached a desired temperature (usually from 400°F-700°F) for a desired time. The oven retains the heat from the fire and
So how did we come up with the idea to build this project?
"[Liz
text] "
-Liz
"I
actually wanted to build a cob oven for a long time. I had the opportunity to
work on a cob session on one last year which sparked my interest. Originally I
wanted to build one on city property, but that would have taken a long time to
approve (perhaps I'll save it for a senior project). I was able to join this
project after Liz had already submitted the proposal. Liz said an extra hand on
the project would help out a lot because there's a lot more than just the
construction part, there's a lot of planning and preparation as well - it's a
lot for a person to do on their own.
Also, I wanted to build something of lasting value. A cob oven would serve many people, especially in a place of public view, and last for a long time." - John
Where were we planning to build a structure that could last half a century? Read on to find out.
¿To·ma·to/To·mah·toe?
What's the difference between a Cob Oven and an Earthen Oven?
Cob Ovens (sometimes spelled Cobb to preserve it's Old English origin) are ovens made of a cob mixture containing the three specific elements of clay, sand, and straw.
The word cob traced to it's origin meant "lump" or "to lump." (I think of cobble stone streets, perhaps they meant lumpy streets.) Cob is applied in lumps to a certain height, allowed to harden, then the application continues.
Earthen Ovens (sometimes called Earth Ovens for ease of speaking) are ovens made of materials gathered from the earth. This may include clay, sand and straw or other fibrous materials (such as paper or horse manure).
Though the earthen mixture may be applied in lumps, it may not contain specifically clay, sand and straw.
So, while all cob ovens are earthen ovens, not all earthen ovens are cob ovens